This work is aimed at understanding meiotic transvection, a mechanism of gene regulation that controls gene expression in chromosome pairing-dependent manner. Neurospora is a particularly attractive system for this study because it is the only microorganism in which transvection has been observed and the only organism of any kind in which transvection has been observed in meiosis. The long term objective of this research is to understand how meiotic transvection works, to identify the components of its molecular machinery, and to investigate if this chromosome pairing-dependent mechanism of gene regulation exists in other eukaryotes. Our studies on the molecular basis of chromosome pairing- dependent gene control in Neurospora are expected to aid our understanding of similar mechanisms in humans, where they may be responsible for causing disease. To understand meiotic transvection two interrelated projects will be developed. First, the minimal cis-acting signals responsible for the pairing-dependent trans-regulation of the Ascospore maturation-1 (Asm-1+) gene will be determined, and studied, by classical and molecular genetics. These minimal cis-acting signals will then be used to identify Neurospora proteins that bind to this DNA fragment. Second the transcriptional and post- transcriptional regulation of paired and unpaired copies of Asm- 1+ during sexual development will be studied, and the molecular basis of the dominant behavior of unpaired copies of the gene will be determined. Our understanding of the molecular mechanisms, and of the cellular components involved in meiotic transvection will contribute to the identification, study and understanding of mechanisms of gene control based on diploidy, the dominant phase of most eukaryotes.